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So, I have been toying with the possibility that nobody may
win the N-Prize, leaving it up to me.
One of the problems with rocket engines, particularly ones
fuelled by LOX and a liquid fuel, is that the combustion
chamber and rocket nozzle usually have to be cooled to
prevent them burning
Traditionally, this is done by circulating either the fuel or
the LOX through pipes on the outer surface of the chamber
and nozzle, on their way to the combustion chamber. This
is quite neat (it cools the critical parts, and pre-heats the
fuel or oxygen), but also complex. It's particularly
problematic for small engines.
So, how to avoid this?
The desirable option would be to line the combustion
chamber and nozzle with Starlite, a heatproofing
compound of truly remarkable fortitude (linky). However,
the inventor is dead, and during his lifetime he never
revealed the secret of its composition, except to his
So, Plan B. What happens if you take a conventional
rocket combustion chamber, and cut a slot in it,
circumferentially, near the top, to let air in?
Obviously, when the rocket is sitting on the launch pad
firing away, hot exhaust gasses will come out of this slot,
and it will all be a bit of a waste. However, once the
rocket is travelling at speed, air should be forced into the
slot instead. This air would form a boundary layer around
the hot gases, effectively working as a barrier between the
gases and the walls of the chamber and nozzle.
There are obviously some issues here, because the
combustion chamber is, necessarily, at very high pressure.
Hence, an air scoop might be needed to pressurize the
oncoming air and force it through the slot.
Ultimately, this design sort of approaches a ramjet, except
that the oxidiser is LOX rather than the inrushing air itself.
It also sort of nods toward an aerospike design, where the
surrounding air performs the function of a containing
A few mm keeps an egg uncooked after 3min in a blowtorch flame. [MaxwellBuchanan, Sep 05 2012]
What this is a reinvention of [notexactly, Jan 14 2016]
||Can you get enough air at the altitude the engine will be travelling through to act as a cooling agent? Would richening the mixture work like it does on piston engines?
There is a flux for welding thin stainless exhaust tubing for racing engines that is applied to the back of the joint and becomes glass-like during the weld preventing burn through and weld drooping on the inside of the joint.
The product in the video needs to be located. From the family?
||//Can you get enough air...?//
||Good question. However, the rocket is
accelerating, which would scoop in more air,
perhaps compensating for the lower atmospheric
||//Would richening the mixture work like it does
on piston engines? // I don't know. But this
would seem to rely on incomplete combustion to
reduce temperatures inside the chamber and
nozzle, which would lower efficiency.
||//However, the inventor is dead, and during his lifetime he never revealed the secret of its composition, except to his family.//
||If samples have been given to NASA then its composition should be known.
Aerogel powder maybe?
||//which would lower efficiency//
Agreed, this is a crutch sometimes used on piston engines.
Has burn time been calculated to be long enough for available nozzle material to fail?
||True rockets are used for orbital lift because
their dwell time in the atmosphere is short,
and once exoatmospheric there is no air
||On the pad, the counterthrust back up your
"scoop duct" will add drag. The scoop will add
and won't work below supersonic
speeds. Plus it will add weight and complicate
the vehicle design.
||I bored NASA with something similar in 2003, a sleeve that extended down from the nozzle, channel air into it via NACA ducts, try and get some ramjet effect off the hot sleeve.
||They have since added an extra-large bin marked "Crank" to deal with my kind...
||Maybe it's just a heat superconductor, to this realm, or another.
||// This is quite neat (it cools the critical parts, and pre-heats the fuel or oxygen), but also complex. //
It's just a big Primus stove, shirley?
||Is it really likely that no one will win the N-Prize?
||//If samples have been given to NASA then its
composition should be known.// The inventor did
not let samples out of his sight, apparently, and
did not give anyone the chance to reverse
engineer the stuff.
||//Has burn time been calculated to be long
enough for available nozzle material to fail?//
Apparently yes. All significant liquid rockets seem
to have cooled chambers and nozzles, and there
are many articles on trying to to find materials
which can be operated uncooled, so it's clearly
still an issue.
||//The scoop will add drag
and won't work below
supersonic speeds// Yes, I was afraid of that. Ah
||//I bored NASA with something similar in 2003//
Great minds think alike.
||//Is it really likely that no one will win the N-
Prize?// Hard to tell. There's one more year to
run (after extending the prize for a final further
year), and a handful of teams look like serious
contenders. But if not, I shall have to buy
earplugs and hard hats for everyone on the Estate,
and get down to some serious foolhardiness.
||//I bored NASA with something similar in 2003// Great minds think alike.
||If that includes me, you can expect a visit from the Trading Standards people very soon.
||OK, so this isn't going to fly.
||How about plan C. Hydrogen peroxide is used as a
monopropellant, and decomposes at a fairly low
temperature. But it's not as good as
||However, suppose you took a regular LOX/fuel
rocket, and added a ring of peroxide injectors
around the edge? Then the decomposing peroxide
would act as a barrier to protect the casing from
the LOX/fuel combustion, but the peroxide would
be adding a fair amount of additional thrust,
rather than being dead weight or drag.
||Let's say that by some perverse quirk of
laminar flow, you can create and maintian a
10mm thick layer of cool, liquid H2O2 on the
surface of the bell.
||But the main combustion is going to be going
on very close, and throwing out quite
staggering amounts of infrared, to which the
peroxide isn't completely opaque. So
although you may reduce input by
conduction, the radiation transfer is still
going to be significant.
||If you could maintain an Argon jacket in the
interior at the same pressure as the exhaust,
that might do some good. The Argon is pretty
non-conductive, and would keep free radicals
away from the walls too.
||//If you could maintain an Argon jacket in the interior//
Is that like a Nylon jacket? Cuz if it is I could donate a
couple to the project.
||Instead of creating a barrier or sacrificial lining to the
nozzles, why not try a design a nozzle which continually
turns inside out for cooling whilst still remaining the
desired shape? Something like a Caterpillar tread or
perhaps a series of roller bearings.
||Argon is pretty well the worst thing to use for coo... hmm... you mean an Argon _layer_, which goes out with the exhaust. Okay, I'm in, but your speed of sound just went down the tubes if you've an H2+O rocket.